This application is based on, and claims priority of, Canadian Patent Application Nos. 2,326,362, filed Nov. 20, 2000; 2,327,862, filed Dec. 6, 2000; and 2,342,719, filed Apr. 2, 2001.
Not Applicable.
1. Technical Field
The present invention relates to optical signal processing devices, and in particular to wavelength-dependent optical signal processing devices incorporating an angle-to-offset module.
2. Background of the Invention
In the modern communications network space, the use of wavelength division multiplexed (WDM) and dense wavelength division multiplexed (DWDM) optical signals are becoming increasingly popular. As is well known in the art, wavelength division multiplexing involves the transmission of multiple light beams through a single waveguide or optical fiber. Each light beam (which is commonly referred to as a channel) generally has a narrow range of wavelengths centered on a nominal channel or center wavelength, and normally conveys a respective stream of data traffic.
At a minimum, practical implementation of wavelength division multiplexing requires optical components capable of optically multiplexing each channel into a single waveguide, and then optically demultiplexing each of the channels from that waveguide. Conventionally, other channel-specific signal processing, such as signal regeneration; Add-Drop Multiplexing (ADM); channel equalization; gain equalization; and channel switching, have been performed electronically. That is, each channel is converted into an electronic signal, processed using conventional electronic means, and then converted back into optical signals for transmission. At lower data rates (e.g., approx. 2.5 GHz), such electronic processing systems can be cost effective. However, as data rates increase (e.g., beyond about 10 GHz), electronic signal processing systems become increasingly expensive, because of physical limitations inherent to electronic systems. Thus optical signal processing systems capable of performing complex channel-specific signal processing functions entirely in the optical domain are increasingly in demand.
Optical signal processing modules (e.g., Add-Drop Multiplexers (ADMs); Dynamic Channel Equalizers (DCEs); and switches) are known. These modules conventionally require complex opto-mechanical layouts (in which the involved optical components are not located on a common optical axis) in order to achieve the spatial separations needed to perform the desired function. The physical size and complexity of these modules increases the difficulty of maintaining adequate precision during manufacture. This inevitably results in increased costs.
Accordingly, an optical signal processing module, in which channel-specific optical signal processing can be accomplished using a simple component layout and small physical size, remains highly desirable.
Accordingly, an object of the present invention is to provide an optical signal processing module capable of channel-specific optical signal processing using a simple, physically compact component layout.
Accordingly, an aspect of the present invention provides an optical device for wavelength dependent processing of optical signals. The optical device comprises a dispersion element, a reflector, and an angle-to-offset (ATO) element. The angle-to-offset (ATO) element has at least one focal plane having a focal length approximately equal to a near zone length or Rayleigh range of the beam of light incident on the ATO element. The dispersion element is adapted to separate an input wavelength division multiplexed (WDM) light beam received from an input port of the optical device into two or more channel light beams. The reflector is arranged to receive the channel light beams from the dispersion element via the ATO element. The reflector is designed to reflect at least one of the channel light beams toward a respective output port of the optical device. With this arrangement, the dispersion element, reflector and ATO element cooperate to demultiplex the input WDM light beam optically. Additional optical elements arranged in the propagation path between the reflector and the output port(s) and/or between the input port and the dispersion element can be used to provide further optical signal processing functionality, as well, the reflector can be modified to change functionality.
The dispersion element may be provided as a diffraction grating disposed in or near a focal plane of the ATO element.
The ATO element may be either a curved mirror having a focal plane, or a refractive lens. In the case of a mirror, both the dispersion element and the reflector are disposed in or near the focal plane. In the case of a lens, the dispersion element and the deflector are disposed in or near respective opposite focal planes of the lens.
In some embodiments, the reflector comprises an array of two or more reflective elements disposed in or near a focal plane of the ATO element. Each reflective element can be arranged in a propagation path of a respective channel light beam from the dispersion element, via the ATO element.
In some embodiments, each reflective element is fixed. The reflective elements may be oriented at a common angle, or at a respective unique angle with respect to the dispersion plane of the dispersion element. In other embodiments, each reflective element is independently movable, either under analog control or bi-stable. In either case, each reflective element may be provided as either a mirror or a total internal reflection (TIR) element. In some embodiments, each TIR element may be independently controllable to selectively frustrate (or otherwise inhibit) reflection of light.
In some embodiments, an optical switch is provided for switching each channel light beam to a selected output waveguide. The optical switch preferably includes first and second MEMS arrays, each of which are disposed in or near a focal plane of the ATO element.